Increasingly more and more attention is being paid to the area of aging; particularly those aspects of aging which seem to underlie the decline in information processing associated with old age. Although many factors may ultimately be shown to be involved, an increasing body of data strongly suggests that changes in specific aspects of central cholinergic functioning may underlie many of the deficits seen in performance on a variety of behavioral tasks. In addition, selective changes in the circulation of the central nervous system (including both flow and vascular permeability) may be correlated with changes in cognitive performance. Therefore, the primary goal of this project is to study the effects of aging on cholinergic and cerebrovascular functioning in male Sprague-Dawley rats. Individual groups of young, middle-aged, and old rats will be run through a select battery of behavioral tasks designed to provide information concerning each animal's general activity level, learning, and long-term memory capabilities. In addition, a thorough analysis of individual aspects of cholinergic functioning, and regional cerebral blood flow and permeability of the blood brain barrier will be conducted. As a significant amount of the research in aging is conducted with animals, it is extremely important that the animal model upon which we base our conclusions be appropriate for the types of questions being asked. There is, however, some reason to suspect that the animal model has not adequately taken into account the interaction between the changes in brain function and cognition that normally occur as a result of aging and those produced as a result of prolonged exposure (rearing) in restricted environments. Therefore, an additional goal of this project is to determine whether the housing environment (i.e., rearing in standard versus enriched housing conditions) will affect the 1) age-related changes in, and 2) interrelationships between cognitive performance cholinergic functioning and cerebral circulation. Animals from each age group will, therefore, be housed in either an enriched or a standard housing environment and tested to determine whether housing environment influences the normal age-selected changes in behavior, cholinergic, and cerebrovascular functioning.